Titanium dioxide (TiO₂) thin films are widely employed for photocatalytic and photovoltaic applications where the long lifetime of charge carriers is a paramount requirement for the device efficiency. To ensure the long lifetime, a high temperature treatment is used which restricts the applicability of TiO₂ in devices incorporating organic or polymer components. In this study, we exploited low temperature (100–150 °C) atomic layer deposition (ALD) of 30 nm TiO₂ thin films from tetrakis(dimethylamido)titanium. The deposition was followed by a heat treatment in air to find the minimum temperature requirements for the film fabrication without compromising the carrier lifetime. Femto-to nanosecond transient absorption spectroscopy was used to determine the lifetimes, and grazing incidence X-ray diffraction was employed for structural analysis. The optimal result was obtained for the TiO₂ thin films grown at 150 °C and heat-treated at as low as 300 °C. The deposited thin films were amorphous and crystallized into anatase phase upon heat treatment at 300–500 °C. The average carrier lifetime for amorphous TiO₂ is few picoseconds but increases to >400 ps upon crystallization at 500 °C. The samples deposited at 100 °C were also crystallized as anatase but the carrier lifetime was <100 ps.

Transient absorption spectroscopy is a powerful technique to study the photoinduced phenomena in a wide range of states from solutions to solid film samples. It was designed and developed based on photoinduced absorption changes or that photoexcitation triggers a chain of reactions with intermediate states or reaction steps with presumably different absorption spectra. However, according to general electromagnetic theory, any change in the absorption properties of a medium is accompanied by a change in the refractive properties. Although this photoinduced change in refractive index has a negligible effect on solution measurements, it may significantly affect the measured response of thin films. In this Perspective paper, we examine why and how the measured responses of films differ from their expected "pure" absorption responses. The effect of photoinduced refractive index change can be concluded and studied by comparing the transmitted and reflected probe light responses. Another discussed aspect is the effect of light interference on thin films. Finally, new opportunities of monitoring the photocarrier migration in films and studying nontransparent samples using the reflected probe light response are discussed. Most of the examples provided in this article focus on studies involving perovskite, TiO₂, and graphene-based films, but the general discussion and conclusions can be applicable to a wide range of semiconductor and thin metallic films.

Hybrid polymer composites based on poly vinylidene fluoride (PVDF) matrix are fabricated by dispersion of few layered graphene (FLG) and nickel spinal ferrites (NSF) for improving EMI shielding effectiveness. The FLG loading is kept constant at 3 wt% while NSF content is varied from 15–30 wt% in PVDF using solution processing technique. The shielding effectiveness in the frequency domain of 1–12 GHz is enhanced ranging 25 dB–45 dB for PVDF/FLG composite as compared to ∼0 dB for neat PVDF. With addition of NSF up to 15 wt%, the attenuation is increased to 30 dB–53 dB, clearly indicating the effective interaction and network formation of FLG and NSF in PVDF matrix. Moreover, the shielding effectiveness trend is reduced to 12 dB–43 dB as the NSF loading is increased to 30 wt% owing to its agglomeration. Absorption is the dominant phenomena in obtaining the total shielding effectiveness of ∼53 dB for PVDF/FLG-3 wt%NSF-15 wt% hybrid polymer composites. Additionally, the I-V curves provide the electrical conductivity trend while scanning electron microscope (SEM) confirms the network formation in hybrid composite.